Maniac Mansion fan "defgav" has been working on a hack of the game's NES ROM, defiling the game and giving it sort of a new personality. He explains:
It's a NES rom of Maniac Mansion hacked kinda crazy. Most of the text is changed. Some of the graphics are altered.. specifically the characters are ALL JACKED UP! Hence, they are zombies. See.. it kinda plays like a fake sequel: The radiation was so strong the first time the kids saved Sandy that it mutated them into zombies. Now they're out for revenge. The goal is to blow up the house!
Read more about his efforts (which have been going on for five years) in his forum thread
, where you can grab the ROM and run it through your NES emulator of choice.